The present invention relates to bridged zirconocene compounds, to the corresponding ligands, to a new process for their preparation and to the use of said zirconocenes as catalytic components in the polymerization of olefins.
Stereorigid chiral metallocene compounds possessing two bridged indenyl groups are well known in the state of the art and are mainly used as catalytic components in olefin polymerization processes, and in particular in the preparation of stereoregular polyolefins. The numbering of the substituents on the indenyl group, to which reference is made in the present application, in accordance with the IUPAC nomenclature, is the following: 
In the bridged indenyl metallocene compounds known in the state of the art, the indenyl groups are linked together by divalent radicals containing one or more carbon atoms and/or heteroatoms; the divalent bridging groups are generally linked to the 1 position of said indenyl groups, and therefore, the common indenyl metallocenes are 1-indenyl compounds. For example, the European patent application EP 0 485 823 describes a class of bridged bis(1-indenyl) metallocenes, wherein the indenyl groups have a substituent other than hydrogen in the 2 position and are bridged in the 1 position by means of a bridge containing 1 or more carbon atoms (e.g. an ethylene or isopropylidene group) or containing heteroatoms (e.g. a dimethyl-silyl or a diphenyl-silyl group).
The European patent application EP 0 372 414 describes a very broad class of bridged or unbridged metallocenes; among the many metallocenes exemplified, are reported two specific bis-indenyl metallocene compounds, wherein the divalent group bridging the indenyl groups is linked to the 1 position of one indenyl group and to the 2 position of the other indenyl group (formulae II-1 and II-2, on page 5 of said patent application).
The International patent application WO 94/11406 describes a very broad class of metallocene compounds of formula Rxe2x80x2Ind-M-(CP)Qk, wherein: Ind is an indenyl group; Rxe2x80x2 is a substituent, other than hydrogen, linked in the 2 position of said indenyl group; Cp is a cyclopentadienyl group; M is a transition metal belonging to group 3, 4, 5 or 6 of the Periodic Table of Elements; and Q is a "sgr"-ligand of the metal M, k being an integer linked to the valence of said metal M. Among the huge plethora of embodiments envisaged in the reported general formula, Rxe2x80x2 can form a bridge between the 2 position of the Ind group and the Cp group of the above formula; therefore, the class of bis(2-indenyl) compounds is generically described. The definition of the bridging group Rxe2x80x2 is very broad too, the preferred bridges linking the two indenyl residues being xe2x80x94Sxe2x80x94, (CH3)2Si less than  and xe2x80x94CH2xe2x80x94 groups; in fact, in the working examples only bis-indenyl zirconocenes with a one-atom-bridge have actually been synthesized and tested in ethylene (co)polymerization, giving ethylene homopolymers in very low yield and ethylene/propylene copolymers having very low molecular weights and in low yields too.
The Applicant has now unexpectedly found a new class of bridged bis(2-indenyl)zirconocenes, particularly active as catalyst components for the polymerization of olefins. Said zirconocene compounds are characterized by the presence of two indenyl ligands, bridged in the 2 position by means of a two-carbon-atoms divalent group.
Therefore, an object of the present invention is a bridged zirconocene compound of formula (I): 
wherein R1, R2, R3 and R4, the same or different from each other, are selected from the group consisting of hydrogen, linear or branched, saturated or unsaturated, C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containing one or more Si or Ge atoms, or wherein two substituents of R1, R2, R3 and R4 form a ring having from 4 to 8 carbon atoms;
R5 and R6, the same or different from each other, are selected from the group consisting of linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containing one or more Si or Ge atoms, or two vicinal R6 substituents on the same indenyl group form a ring having from 4 to 8 carbon atoms;
m is an integer ranging from 0 to 2; n is an integer ranging from 0 to 4;
the groups X, the same or different from each other, are hydrogen, halogen, xe2x80x94R, xe2x80x94OR, xe2x80x94SR, xe2x80x94NR2 or xe2x80x94PR2, wherein R is selected from the group consisting of linear or branched, saturated or unsaturated, C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containing one or more Si or Ge atoms.
Another object of the present invention is a catalyst for the polymerization of olefins comprising the product obtainable by contacting:
(A) one or more bridged zirconocene compounds of formula (I), as described above, and
(B) a suitable activating cocatalyst.
Furthermore, the present invention provides a process for the polymerization of olefins comprising the polymerization reaction of one or more olefinic monomers in the presence of a catalyst as described above.
Another object of the present invention is a ligand of formula (II): 
wherein R1, R2, R3, R4, R5 and R6, m and n have the meaning reported above, with the proviso that:
when R1, R2, R3 and R4 are hydrogen and n is 0, then m is different from 0; and
when R1, R2, R3 and R4 are hydrogen, n is 0 and m is 1, then R5 is different from xe2x80x94CH3, xe2x80x94CH2Ph and xe2x80x94Si(CH3)3.
The present invention further concerns a process for the preparation of the above ligands of formula (II), comprising the following steps:
(1) reacting an adipic ester of formula (III) with at least 2 equivalents of a benzyl compound of formula (IV) and at least 2 equivalents of an alkali metal or alkaline earth metal base, in the presence of an organic solvent, to obtain an intermediate compound of formula (V); said step may be represented by the following reaction scheme: 
xe2x80x83wherein R1, R2, R3, R4, R6 and n have the meaning reported above, R7 is selected from the group consisting of linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, and Y is a suitable leaving group;
(2) cycling said compound of formula (V) to obtain a compound of formula (VII); said step may be represented by the following reaction scheme: 
xe2x80x83wherein R1, R2, R3, R4, R6 and n have the meaning reported above and Yxe2x80x2 is a suitable leaving group;
(3) reducing the ketonic functions of the indanyl moieties of the compound of formula (VII) to obtain the diol (VIII) and finally dehydrating the hydroxy functions of the indanyl moieties of said diol (VIII) to give the ligand (II); said step may be represented by the following reaction scheme: 
xe2x80x83wherein R1, R2, R3, R4, R6 and n have the meaning reported above.
When in the ligand of formula (II) m is xe2x89xa0 0, then the substituents R5 can be introduced on the cyclopentadienyl ring by reacting a compound of formula (VII) or the same ligand of formula (II) with a suitable amount of an alkylating agent R5MgBr, R5MgCl or R5jB, wherein B is an alkaline or alkaline-earth metal, and j is 1 or 2.
Finally, the present invention concerns intermediate compounds of formula (V), as reported above, useful in the synthesis of the ligands (II), according to the present invention.
The bridged zirconocene compounds of formula (I), the corresponding ligands, the process for their preparation and the catalysts for the polymerization of olefins containing them, according to the present invention, will be better described in the following detailed description.
It is an object of the present invention a bridged zirconocene compound of formula (I), wherein R1, R2, R3 and R4, the same or different from each other, are selected from the group consisting of hydrogen, linear or branched, saturated or unsaturated, C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containing one or more Si or Ge atoms, or wherein two substituents of R1, R2, R3 and R4 form a ring having from 4 to 8 carbon atoms. Preferably R1, R2, R3 and R4 are selected from the group consisting of hydrogen, methyl, ethyl, propyl, phenyl and benzyl; more preferably, R1, R2, R3 and R4 are hydrogen and the bridging group of the two 2-indenyl groups is ethylene.
In the bridged zirconocene compounds of formula (I), R5 and R6, the same or different from each other, are selected from the group consisting of linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containing one or more Si or Ge atoms; or two vicinal R6 substituents on the same indenyl group form a ring having from 4 to 8 carbon atoms. R5 and R6 are preferably selected from the group consisting of methyl, ethyl, propyl, phenyl and benzyl.
The variable m is an integer ranging from 0 to 2; the variable n is an integer ranging from 0 to 4.
The groups X, the same or different from each other, are hydrogen, halogen, xe2x80x94R, xe2x80x94OR, xe2x80x94SR, xe2x80x94NR2 or xe2x80x94PR2, wherein R is selected from the group consisting of linear or branched, saturated or unsaturated, C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containing one or more Si or Ge atoms. X is preferably Cl, Br or methyl.
Non-limiting examples of bridged zirconocene compounds according to the present invention are:
1,2-ethylene-bis(2-indenyl)zirconium dichloride and dimethyl,
1,2-ethylene-bis(1,3-dimethyl-2-indenyl)zirconium dichloride and dimethyl,
rac- and meso-1,2-ethylene-bis(-methyl-2-indenyl)zirconium dichloride and dimethyl,
rac- and meso-1,2-ethylene-bis(1-ethyl-2-indenyl)zirconium dichloride and dimethyl,
rac- and meso-1,2-ethylene-bis(4-phenyl-2-indenyl)zirconium dichloride and dimethyl,
rac- and meso-1,2-ethylene-bis(1-methyl-4-phenyl-2-indenyl)zirconium dichloride and dimethyl,
rac- and meso-1,2-ethylene-bis(1-isopropyl-4-phenyl-2-indenyl)zirconium dichloride and dimethyl.
Said bridged zirconocene compounds can be prepared by reaction of the corresponding ligands of formula (II) first with a compound capable of forming a delocalized anion on the cyclopentadienyl ring, and then with a compound of formula ZrZ4, wherein the substituents Z, the same or different from each other, are halogen (ZrCl4 is particularly preferred), according to common procedures known in the state of the art.
When, in the zirconocene of formula (I) one or more X groups are other than halogen, it is necessary to substitute one or more halogens Z of the zirconocene dihalide with one or more substituents X other than halogen. The substitution reaction can be carried out by standard procedures, known in the state of the art, for example by reacting the zirconocene dihalide with alkylmagnesium halides (Grignard reagents) or with alkyllithium compounds. It is another object of the invention the ligand of formula (II), wherein R1, R2, R3, R4, R5 and R6, m and n have the meaning reported above, with the proviso that:
when R1, R2, R3 and R4 are hydrogen and n is 0, then m is different from 0; and
when R1, R2, R3 and R4 are hydrogen, n is 0 and m is 1, then R5 is different from xe2x80x94CH3, xe2x80x94CH2Ph and xe2x80x94Si(CH3)3.
In fact, ethylene-bridged bis-2-indenyl ligands, unsubstituted or bearing a substituent xe2x80x94CH3, xe2x80x94CH2Ph or xe2x80x94Si(CH3)3 have been disclosed by Nantz M. H. et al. in Organometallics 1993, 12:5012-5015 and by Hitchcock S. R. et al. in Organometallics 1995, 14:3732-3740. These ligands were used to prepare the corresponding titanocene dichloride, useful in the catalytic epoxidation of unfunctionalized alkenes. The ligands mentioned above are expressly excluded from the ligands according to the present invention.
The ligands of formula (II), according to the present invention, are prepared by means of a very simple and efficient process, which employs cheap starting materials and comprises single reaction steps having very high yields, some of them almost quantitative. Furthermore, said process does not require laborious and time-consuming purification procedures, being particularly suitable to large scale production.
The process step (1) comprises reacting the adipic ester of formula (III) with at least 2 equivalents, and preferably 2-4 equivalents of a benzyl compound of formula (IV) and at least 2 equivalents, and preferably 24 equivalents of an alkali metal or alkaline earth metal base, according to the reaction scheme reported in the summary of the invention, to obtain an intermediate compound of formula (V).
Said reaction is preferably carried out one pot, by sequential addition of said base and of the benzyl compound of formula (IV), in the presence of an organic solvent, at a temperature preferably ranging from 20 to 80xc2x0 C., and more preferably from 50 to 70xc2x0 C.
Said base of an alkali metal or alkaline earth metal is preferably selected from the group consisting of NaOEt, KOEt, KOH, NaOH, NaH, KH and mixtures thereof.
Said organic solvent is preferably selected from the group consisting of THF, glyme, toluene and mixtures thereof.
In said compound of formula (IV), Y is preferably Cl or Br.
Reaction step (2) comprises cycling the compound of formula (V), according to the reaction scheme reported in the summary of the invention, to obtain a compound of formula (VII). According to a preferred embodiment of the process of the invention, said step is conducted first de-esterifying the functions xe2x80x94COOR7 of the compound of formula (V) to the corresponding xe2x80x94COOH groups, by adding at least 2 equivalents, and preferably 2-3 equivalents, of a base in a mixture of aqueous and organic solvent.
Said base is preferably KOH and/or NaOH. Said mixture of solvents is preferably a mixture of MeOH and water.
The present reaction step is preferably carried out at a temperature ranging from 20 to 150xc2x0 C., and more preferably from 70 to 100xc2x0 C., for a time of 1-5 hours, and more preferably for 2-3 hours.
The obtained diacid can be isolated by acidification, according to procedures known in the state of the art, and is subsequently derivatized with a suitable leaving group Yxe2x80x2, to give a compound of formula (VI). Said group Yxe2x80x2 is preferably Cl or Br.
When Yxe2x80x2 is Cl, the compound of formula (VI) can be obtained from the above mentioned diacid by reaction with SOCl2 in excess, and preferably in amounts ranging from 6 to 10 equivalents per leaving group Yxe2x80x2, at a temperature preferably ranging from 20 to 80xc2x0 C., and more preferably from 50 to 60xc2x0 C., for a period preferably of 4-12 hours, and more preferably of 7-9 hours.
The compound of formula (VI) is then cycled to give the final compound (VII), in the presence of at least 1 equivalent of a Lewis acid, and preferably 1.1-1.3 equivalents of AlCl3, at a temperature preferably ranging from 0 and 40xc2x0 C., in the presence of an organic solvent. The compound (VII) can be finally isolated from the reaction mixture according to standard procedures.
Reaction step (3) comprises reducing the ketonic functions on the indanyl moieties of the compound of formula (VII) to obtain the diol (VIII) and finally dehydrating the hydroxy functions on the indanyl moieties of said diol (VIII) to give the ligand (II), according to the reaction scheme reported in the summary of the invention.
The compound (VII) can be reduced to the diol (VIII) by reaction with at least 0.5 equivalents, and preferably 1-1.2 equivalents, of a suitable reducing agent, in an organic solvent.
Said reducing agent is preferably selected from the group consisting of NaBH4, LiAlH4, NaH and KH; said organic solvent is preferably MeOH. This reaction is preferably carried out at a temperature ranging from xe2x88x9220xc2x0 C. to 20xc2x0 C., for a time of 10-18 hours. The diol (VIII) can be then isolated by acidification, according to procedures known in the state of the art.
Said diol (VIII) is subsequently dehydrated to the ligand (II) by acid treatment or by thermolysis; in the former case, the diol (VIII) is preferably treated with catalytic amounts of an acid, more preferably p-toluensulfonic acid or HCl, in an organic solvent such as ether, toluene and CH2Cl2, at a temperature ranging from 20 to 100xc2x0 C. In the latter case, the diol (VIII) is preferably dehydrated by thermolysis at a temperature ranging from 200 to 300xc2x0 C., and more preferably from 250 to 270xc2x0 C., for a period of 1-2 hours. The final ligand (II) can be then isolated according to standard procedures known in the state of the art. When in the ligand of formula (II) m is xe2x89xa0 0, then the substituents R5 can be introduced on the cyclopentadienyl ring by reacting a compound of formula (VII) or the same ligand of formula (II) with a suitable amount of an alkylating agent R5MgXxe2x80x2 or R5jB, wherein, Xxe2x80x2 is halogen, B is an alkaline or alkaline-earth metal and j is 1 or 2.
Preferably, the compound of formula (VII) or (II) is reacted with at least 2 equivalents of said alkylating agent, at a temperature ranging from xe2x88x9278xc2x0 C. to 20xc2x0 C., for a time of 1-3 hours. The reaction is preferably conducted in an organic solvent selected from the group consisting of THF, Et2O, toluene and mixtures thereof. Said alkylating agent is preferably selected from the group consisting of R5MgBr, R5MgCl, R5Li, R52Mg and R52Zn.
The ligands of formula (II) according to the present invention can be easily transformed into the corresponding zirconocenes by using standard procedures known in the state of the art. Another object of the present invention are intermediate compounds of formula (V), useful in the synthesis of the ligands of formula (II): 
wherein R1, R2, R3, R4, R5, R6, R7 and n have the meaning reported above.
The bridged zirconocene compounds according to the present invention can be advantageously used as catalytic components for the polymerization of olefins. Therefore, another object of the present invention is a catalyst for the polymerization of olefins, comprising the product obtainable by contacting the following components:
(A) one or more bridged zirconocene compounds of formula (I), as described above, and
(B) a suitable activating cocatalyst.
Activating cocatalysts suitable as component (B) in the catalysts of the invention are linear, branched or cyclic alumoxanes, containing at least one group of the type: 
wherein the substituents R8, the same or different from each other, are linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl, C7-C20 arylalkyl radicals, or groups xe2x80x94Oxe2x80x94Al(R8)2.
Examples of alumoxanes suitable as activating cocatalysts in the catalysts according to the present invention are methylalumoxane (MAO), tetra-isobutyl-alumoxane (TIBAO), tetra-2,4,4-trimethylpentylalumoxane (TIOAO) and tetra-2-methyl-pentylalumoxane. Mixtures of different alumoxanes can also be used.
Activating cocatalysts suitable as component (B) in the catalysts of the invention are also the products of the reaction between water and organometallic aluminum compounds, preferably of formula AlR83 or Al2R86, wherein R8 has the meaning reported above.
Particularly suitable are the organometallic aluminum compounds of formula (II) described in EP-A-575,875 and those of formula (II) described in WO 96/02580. Non-limiting examples of organometallic aluminum compounds of formula AlR83 or Al2R86 are:
tris(methyl)aluminum, tris(isobutyl)aluminum, tris(isooctyl)aluminum bis(isobutyl)aluminum hydride, methyl-bis(isobutyl)aluminum, dimethyl(isobutyl)aluminum, tris(isohexyl)aluminum, tris(benzyl)aluminum, tris(tolyl)aluminum, tris(2,4,4-trimethylpentyl)aluminum, bis(2,4,4-trimethylpentyl)aluminum hydride, isobutyl-bis(2-phenyl-propyl)aluminum, diisobutyl-(2-phenyl-propyl)aluminum, isobutyl-bis(2,4,4-trimethyl-pentyl)aluminum and diisobutyl-(2,4,4-trimethyl-pentyl)aluminum.
Particularly preferred aluminum compounds are tris(2,4,4-trimethylpentyl)aluminum (TIOA), and triisobutylaluminum (TIBA).
Mixtures of different organometallic aluminum compounds and/or alumoxanes can also be used.
The molar ratio between aluminum and the metal of the zirconocene is preferably comprised between about 10:1 and about 50,000:1, and preferably between about 100:1 and about 4,000:1.
Further activating cocatalysts suitable as component (B) in the catalysts of the invention are those compounds capable of forming an alkyl zirconocene cation. Non-limiting examples of these compounds are those of formula Y+Zxe2x88x92, wherein Y+ is a Bronsted acid capable of donating a proton and of reacting irreversibly with a substituent X of the compound of formula (I), and Zxe2x88x92 is a compatible anion which does not coordinate, which is capable of stabilizing the active catalytic species originating from the reaction of the two compounds, and which is sufficiently labile to be able to be displaced from an olefinic substrate. The Zxe2x88x92 anion preferably comprises one or more boron atoms.
More preferably, the Zxe2x88x92 anion is an anion of formula BAr4(xe2x88x92), wherein the Ar substituents, the same or different from each other, are aryl radicals such as phenyl, pentafluorophenyl, bis(trifluoromethyl)phenyl. Tetrakis-pentafluorophenyl-borate is particularly preferred. Moreover, compounds of formula BAr3 can be used conveniently.
The catalysts of the present invention can also be used on inert supports. This is achieved by depositing the zirconocene compound (A), or the product of its reaction with the activating cocatalyst (B), or component (B) and then the zirconocene compound (A), on inert supports such as silica, alumina or olefin polymers or prepolymer such as polyethylenes, polypropylenes or styrene-divinylbenzene copolymers. The thus obtained solid compounds, in combination with further addition of alkyl aluminum compound either untreated or pre-reacted with water, if necessary, is used advantageously in gas-phase polymerization.
The present invention also provides a process for the polymerization of olefins comprising the reaction of polymerization of one or more olefinic monomers in the presence of a catalyst as described above. Representative examples of olefinic monomers which may be used in the polymerization process of the invention are ethylene, xcex1-olefins such as propylene and 1-butene, cycloolefins and conjugated diolefins.
The catalysts of the invention can be advantageously used in ethylene homopolymerization or in the copolymerization of ethylene with propylene, 1-butene, 1-hexene, 4-methyl-1-pentene or 1-octene. Said catalysts unexpectedly allow to obtain, in high yields, ethylene polymers having very low molecular weights and having narrow molecular weight distributions (MWDs), without the need of using substantial amounts of molecular weight regulators, such as hydrogen. In particular, with the catalysts of the invention it is possible to obtain, with high yields and without the use of molecular weight regulators, ethylene homopolymers or ethylene/xcex1-olefin copolymers having intrinsic viscosities (I.V.) lower than 1.0 dl/g, preferably comprised between 0.2 and 0.8 dl/g, more preferably between 0.3 and 0.7 dl/g; furthermore, the obtained polymers have a molecular weight distribution MWD (Mw/Mn) lower than 3.
The catalysts of the invention not always show satisfactory activities in the homopolymerization of propylene to give atactic propylene oligomers. However, when the homopolymerization of propylene is performed in the presence of hydrogen, a very large increase in the activities is unexpectedly observed.
Therefore, according to another particular embodiment, the present invention provides a process for propylene homopolymerization, carried out in the presence of controlled amounts of hydrogen, which lead to a significant 100-500 fold increase in homopolymerization activity. The amount of hydrogen is preferably comprised between 1 mol % and 30 mol %, with respect to the total quantity of hydrogen and propylene, at the temperature of 50xc2x0 C.; said amount of hydrogen is more preferably 2-3 mol % of a total amount of hydrogen and propylene.
The polymerization process according to the present invention can be carried out in the liquid phase, in the presence or absence of an inert hydrocarbon solvent, or in the gas phase. The hydrocarbon solvent can be either aromatic, such as toluene, or aliphatic, such as propane, hexane, heptane, isobutane and cyclohexane.
The polymerization temperature is generally comprised between xe2x88x92100xc2x0 C. and +250xc2x0 C., and more particularly between xe2x88x9250xc2x0 C. and +100xc2x0 C. The lower is the polymerization temperature, the higher are the molecular weights of the polymers obtained.
The molecular weight of the polymers can be further varied by changing the type or the concentration of the catalytic components or by using molecular weight regulators, for example hydrogen. Nevertheless, we stress again that the gist of the catalysts of the invention and of the polymerization process using them is the obtainment of polymers having a very low molecular weight, as well as a narrow MWD, which allow to avoid the presence of low soluble fractions in the final polymer.
The MWD can be varied by using mixtures of different zirconocene compounds, or by carrying out the polymerization in several steps that differ with respect to the temperatures of polymerization and/or the concentrations of molecular weight regulator.
The polymerization yields depend on the purity of the zirconocene component of the catalyst. Accordingly, the zirconocene compounds obtained by the process of the invention can be used as they are, or they can undergo purification treatments.
The components of the catalyst can be brought into contact with each other prior to polymerization. The duration of contact is generally between 1 and 60 minutes, preferably between 5 and 20 minutes. The pre-contact concentrations for the zirconocene component (A) are between 10xe2x88x922 and 10xe2x88x928 mol/l, whereas for component (B) they are between 10 and 10xe2x88x923 mol/l. Precontact is generally effected in the presence of a hydrocarbon solvent and, if necessary, of small amounts of monomer.
The following experimental examples are given for illustrative and not limiting purposes.
All the operations with the catalytic systems, the metallocenes and the aluminum alkyls were carried out under nitrogen atmosphere.
The zirconocenes and their intermediates were characterized by the following methods:
The 1H-NMR and 13C-NMR spectra were recorded in CD2Cl2 (referenced against the middle peak of the triplet of residual CHDCl2 at 5.35 ppm) and C6D6 (referenced against residual C6D5H at 7.15 ppm), using a Varian Gemini 300 (1H NMR at 300 MHz, 13C NMR at 75.4 MHz) or a Varian XL 200 (1H NMR at 200 MHz, 13C NMR at 50.1 MHz).
All NMR solvents were dried over 4 xc3x85 molecular sieves before use. Preparation of the samples was carried out under nitrogen, using standard inert atmosphere techniques; the measurements were performed at 20xc2x0 C.
All the polymerization solvents were used after drying over molecular sieves and deoxygenated; ethylene was used as polymerization grade reagent; 1-hexene was dried over alumina and distilled over LiAlH4. The polymers were characterized by the following methods:
Intrinsic viscosities I.V. were measured at 135xc2x0 C. in tetrahydronaphtalene (THN) or in decalin.
Calorimetric measurements were performed by using a differential scanning calorimeter Perkin Elmer DSC-7. The instrument was calibrated with indium and tin standards. Weighted sample (5-10 mg) was sealed into aluminum pans, heated to 200xc2x0 C. and kept at that temperature for a time enough (5 minutes) to allow a complete melting of all the crystallites. Successively, after slow cooling at 20xc2x0 C./min to 0xc2x0 C., the peak temperature was assumed as crystallization temperature (Tc). After standing 5 minutes at 0xc2x0 C., the sample was heated to 200xc2x0 C. at a rate of 10xc2x0 C./min. In this second eating run, the peak temperature was assumed as melting temperature (Tm) and the area as global melting enthalpy (xcex94Hf).
Molecular weights (Mw) and molecular weight distributions (Mw/Mn) were determined by SEC analysis performed by using a xe2x80x9cWATERS 200xe2x80x9d GPC instrument, working at 135xc2x0 C. in 1,2-dichlorobenzene stabilized with BHT (2,6-di-t-butyl-4-methyl-phenol) 0.1 wt %.
The amounts of 1-hexene (C6) units in the ethylene/1-hexene copolymers were determined at 120xc2x0 C. by a Brucker AC-200 spectrometer operating at 200.13 MHz in the Fourier Transform mode. The powder polymer samples were dissolved in 1,1,2,2-tetrachloro-1,2-dideuteroethane (C2D2Cl4) to give an 8% w/v. concentration. Peak assignments and composition calculations were made according to the method described by H. C. Cheng et al. in Polymer. Bull. (vol.26, page 325, 1991). The triad and dyads distributions, as well as the kinetic parameters r1 and r2 were calculated by 13C-NMR analysis, according to the method described by T. Uozumi and K. Soga (Macromol. Chem., 193:823, 1992).
The characterization of the propylene polymers and the determination of the amount of propylene (C3) units in ethylene/propylene copolymers were carried out on a Brucker 500 spectrometer, operating at 125.4 MHz. The samples were dissolved in 1,2,4-trichlorobenzene with some 1,4-dichloro-deuterohexene (1,4-C6D4Cl2) added as lock. The measurements were done in 5 mm NMR tubes at 130xc2x0 C., with a 70xc2x0 pulse and a relaxation delay of 15 seconds. The characterization of ethylene/propylene copolymers was made according to the method described by Y. Doi et al. in Makromol. Chem. Rapid Comm. (vol.4, page 169, 1983).
Methylalumoxane (MAO)
A commercial (Witco, MW 1400) 10% w/w toluene solution of MAO was dried in vacuum, at 60xc2x0 C., to obtain a white free-flowing powder. Said powder was solubilized in toluene (1M solution) before use.
Tris(2,4,4-trimethyl-pentyl)aluminum (TIOA)
The product commercially available from WITCO was used diluted to a 1 M solution in heptane.
Tris(2-methyl-propyl)aluminium (TIBAL)
The commercial product was purchased from Witco and used as a 1M solution in hexane.
1,2-ETHYLENE-BIS(2-INDENYL)ZIRCONIUM DICHLORIDE
(a) Preparation of the ligand 1,2-bis(2-indenyl)ethane
Preparation of the diethyl ester of 2,5-dibenzyl-adipic acid from diethyl adipate 
487 g of NaOEt (6.87 mol, 1.2 equivalents) were suspended in 3.54 kg of THF, in a 10 L cylindrical double-walled glass reactor, equipped with overhead stirrer and oil heating/cooling bath. The obtained suspension was heated to 60xc2x0 C. and 1170 g (5.73 mol) of diethyl adipate were added, over a period of 1 hour.
The reaction mixture was stirred for 16 hours, at 60xc2x0 C., and 820 g (6.41 moles, 1.12 equivalents) of benzyl chloride were added, over a period of 3.75 hours. The resulting product, the diethyl ester of 2-benzyl adipic acid, was maintained under stirring for other 3.5 hours, at 60xc2x0 C., and the mixture was then allowed to cool to room temperature. 487 g (6.87 moles, 1.2 equivalents) of NaOEt were added to the mixture, over a period of 2 hours, at 23xc2x0 C., and the reaction was then slowly warmed to 60xc2x0 C., for 4 hours, and finally stirred for 16 hours at 60xc2x0 C.
To the thus obtained mixture were then added 879 g (6.87 moles, 1.2 equivalents) of benzyl chloride, over a period of 1.75 hours. The reaction mixture was stirred at 65xc2x0 C. for 6 hours and then cooled to 30xc2x0 C.; an additional 100 g (1.47 moles) of NaOEt were added and, after 5 hours at 60xc2x0 C., further 207 g (1.62 moles) of benzyl chloride were added, over a period of 1.75 hours, in order to convert the unreacted NaOEt into PhCH2OEt. After 2 hours at 60xc2x0 C., to the obtained mixture were added 224 g (4.87 moles, 0.85 equivalents) of EtOH and the reaction mixture was allowed to cool to 25xc2x0 C. After the addition of 2,800 ml dilute HCl (pH 2), 1.43 kg toluene were added and the organic and aqueous layers were separated. The solvents were removed on a rotary evaporator and the higher boiling fractions (namely the excess of benzyl chloride and benzyl ether) were removed on a Schlenk line, at 100xc2x0 C.
This purification procedure gave 2,035 g of dibenzyl adipate, having a purity of 95% (92% yield).
1H NMR (CDCl3): xcex4 7.37-7.1 (m, 10H), 4.04 (q, 4H, CH2), 2.9 (m, 2H), 2.7 (m, 2H), 2.6 (m, 2H), 1.65 (m, 2H), 1.55 (m, 2H), 1.13 (t, 3H, Me), 1.125 (t, 3H, Me). 13C NMR (CDCl3): xcex4 174.8 and 176.26 (COOH, diastereomers), 138.86 (C), 128.6 (CH), 128.06 (CH), 126.06 (CH), 59.91 (CH2), 47.17 and 46.88 (CH, diastereomers), 38.18 and 38.03 (CH2, diastereomers), 29.28 and 29.18 (CH2, diastereomers), 13.90 (Me).
De-esterification of the diethyl ester of 2,5-dibenzyl-adipic acid 
In a 3 L 3-neck round bottom flask, equipped with an overhead stirrer, were added 723 g (1.89 moles) of diethyl ester of 2,5-dibenzyl-adipic acid, obtained as described above, and 910 ml (5.67 moles) of Claisen alkali solution (a 6.25M solution of KOH in a 1:3/H20:MeOH (v/v) mixture) and the obtained mixture was heated to 90xc2x0 C. After 3 hours, the reaction mixture was cooled and transferred to a 2 L flask, and the MeOH was removed on a rotary evaporator. The mixture was then washed with 800 mL ether, in order to remove organic impurities, and the obtained viscous water solution was poured into a 5 L beaker, diluted with 1 L water and cooled using an ice bath, to a temperature of about 10xc2x0 C. To the solution, maintained under constant stirring, was slowly added concentrated HCl, always maintaining the temperature at about 10-15xc2x0 C.
At a pH value of about 3, a copious white/beige powdery precipitate formed; concentrated HCl was added until a pH of 1 to 2 was reached, obtaining a final solution of about 4 L. The white precipitate was isolated by filtration and washed with 300 ml water, thus obtaining 2,5-dibenzyl-adipic acid, as a white powder. After drying in a vacuum oven (at 200 mmHg, under nitrogen stream, at 70xc2x0 C. to remove residual water) to constant weight, 598 g of pure 2,5-dibenzyl-adipic acid were isolated (yield 97% wt.),
1H NMR (CD3OD, 300 MHz): xcex4 7.10 (m, 10H, aromatic), 2.90 (m, 2H), 2.70 (m, 4H), 1.60 (m, 4H) ppm. 1H NMR (d8-THF): xcex4 10.7 (br s, 2H, OH), 7.21-7.08 (m, 10H), 2.9 (dd, 2H), 2.62 (dd, 2H), 2.56 (m, 2H), 1.70 (m, 2H), 1.52 (m, 2H). 13C NMR (d8-THF): xcex4 176.3 and 176.26 (COOH, diastereomers), 140.84 (C), 129.75 (CH), 128.88 (CH), 126.74 (CH), 47.94 and 47.82 (CH, diastereomers), 39.00 and 38.9 (CH2, diastereomers), 30.33 and 30.36 (CH2, diastereomers).
Preparation of 2,5-dibenzyl-adipic acid dichloride 
In a 2 L pear-shaped flask, were added 598 g (1.833 moles) of the 2,5-dibenzyl-adipic acid, prepared as described above, and 2,050 ml of SOCl2 (17.22 mol, density=1.63 g/mL). The obtained mixture was stirred for 16 hours at 20xc2x0 C., and then heated at 55xc2x0 C. for 7 hours, thus giving a homogeneous solution; a rapid but controlled gas evolution was observed. After removal of SOCl2 in excess, under vacuum at a bath temperature of 60xc2x0 C., 300 mL toluene were first added and subsequently removed under vacuum, at 50xc2x0 C., in order to remove any residual SOCl2. A viscous light brown oil was isolated, which proved to be 2,5-dibenzyl-adipic acid dichloride (two diastereisomers were obtained).
1H NMR (CDCl3, 300 MHz): xcex4 7.4-7.2 (m, 8H, aromatic H), 3.14 (m, 4H), 2.87 (m, 2H), 1.80 (m, 4H) ppm.
13C NMR (CDCl3, 75 MHz): xcex4 28.23 (CH2), 28.33 (CH2), 37.48 (CH2), 37.70 (CH2), 58.43 (CH), 58.54 (CH), 127.3 (CH, aromatic), 128.95 (CH, aromatic), 129.06 (CH, aromatic.), 137.1 (C), 176.15 (Cxe2x95x90O) ppm.
Conversion of 2,5-dibenzyl-adipic acid dichloride to the corresponding bis(indanone) 
In a 3 L 3-neck flask, equipped with a large dropping funnel and kept under nitrogen, 605 g (4.53 moles; 24% excess) of AlCl3 (99%, from Aldrich) were suspended in 800 mL of CH2Cl2, previously dried over molecular sieves; to the obtained suspension was slowly added, over a period of 3 hours, the 2,5-dibenzyl-adipic acid dichloride, prepared as described above, previously dissolved in 1200 ml of CH2Cl2. After stirring for 16 hours at 20xc2x0 C., venting away the formed HCl, an orange suspension was obtained. This was carefully poured into a water/ice mixture, in a 5 L beaker, and the yellow CH2Cl2 layer was separated; the aqueous phase was extracted with 4xc3x97250 ml of CH2Cl2. The CH2Cl2 fractions were collected together and dried with anhydrous MgSO4, thus obtaining a clear red-orange solution. Said solution was filtered and the solvent removed in vacuum, to afford a slightly sticky white solid. After washing with 500 ml pentane, 598 g of the bis(indanone) were isolated in the form of a white powder (yield of 93% wt. from 2,5-dibenzyl-adipic acid).
1H NMR (CDCl3, 300 MHz): xcex4 7.7-7.3 (m, 8H, aromatic H), 3.3 (dd, 2H), 2.85 (m, 2H), 2.63 (m, 2H), 2.1 (m, 2H), 1.60 (m, 2H) ppm.
13C NMR (CDCl3, 75 MHz): xcex4 28.6 (CH2), 29.3 (CH2), 32.47 (CH2), 32.69 (CH2), 46.94 (CH), 47.47 (CH), 123.9, 126.65 (CH, aromatic), 127.44 (CH), 134.85, 136.71, 153.78, 208.6 (Cxe2x95x90O) ppm.
Conversion of the above bis(indanone) to the corresponding diol 
In a 5 L beaker, 494 g (1.70 moles) of the bis(indanone) prepared as described above were suspended in 3 L of THF and 1 L MeOH. After cooling the obtained mixture to about 10xc2x0 C., with an ice bath, 71 g (1.87 moles) of NaBH4 were slowly added, over a period of 3 hours, maintaining the suspension under vigorous stirring. The addition of NaBH4 resulted in immediate gas evolution. The reaction mixture was maintained under stirring for 16 hours, at 20xc2x0 C., and then THF and MeOH were removed on a rotary evaporator, thus giving a thick beige slurry. 2 L of water were added to said slurry and the obtained mixture was acidified with dilute HCl till a pH value of 3; a beige powder precipitated and was isolated by filtration. Said powder was extensively washed with water and finally dried to constant weight in a vacuum oven, at 75xc2x0 C., finally obtaining 506 g of diol.
1H NMR (CDCl3, 300 MHz): xcex4 7.05-7.4 (m, 10H, aromatic), 5.13 (d, J=6), 5.05 (dd, J=6), 4.87 (d, J=6) total 2H, 3.1 (m), 2.9 (m), 2.75(m), 2.5(m), 2.4-2.1 (m), 2.0-1.6 (m) ppm.
Dehydration of the diol to give 1,2-bis(2-indenyl)ethane
300 g of the diol, prepared as described above, were placed in a 1 L 3 neck round-bottom flask, in a heating mantel; this was heated to a temperature of about 260xc2x0 C., under nitrogen stream to remove water. The diol melted at about 190xc2x0 C. The thermolysis was stopped after about 2 hours, thus obtaining a product in the form of a xe2x80x9cmelted glassxe2x80x9d; to this product were added 500 ml of CH2Cl2, by stirring and scratching in order to solubilize said melted glass. The resulting mixture was filtered through a frit, thus isolating the insoluble product, that resulted to be 1,2-bis(2-indenyl)ethane. After washing with pentane, 33.7 g of 1,2-bis(2-indenyl)ethane with a purity of 98.95% (GLC analysis) were isolated, in the form of a white powder.
CH2Cl2 was removed under vacuum from the CH2Cl2-soluble fraction, to give a slightly oily orange powder. Said powder was washed with pentane to give 74.4 g of 1,2-bis(2-indenyl)ethane in the form of a 96% pure light beige powder.
Totally were isolated 108.1 g of the desired ligand 1,2-bis(2-indenyl)ethane, with a 42% yield.
1H NMR (CDCl3): xcex4 7.5-7.1 (m, 4H), 6.63 (s, 1H), 3.39 (s, 2H, CH2), 2.86 (s, 2H, CH2).
13C NMR (CDCl3): xcex4 150.1, 145.9, 143.4, 127.1, 126.7, 124.2, 123.8, 120.5, 41.5 (CH2), 31.0 (CH2).
(b) Preparation of the zirconocene dichloride
In a 2 L 3-necks round bottom flask, under nitrogen stream, to 146 g (0.566 moles) of 1,2-bis(2-indenyl)ethane was added 1 L Et2O and the obtained mixture was cooled to xe2x88x925xc2x0 C. by means of a ice/salt bath. To this mixture were slowly added 475 ml of a 2.5 M n-BuLi solution in hexane (2.1 equivalents), over a period of about 2.5 hours. A beige slurry of the dianion was obtained. After having completed the addition, the mixture was stirred for a further 30 minutes, without ice bath, leading to a temperature of 14xc2x0 C.
The volume of the obtained solution was reduced to about 1 L, by removing the solvent under vacuum. This solution was then cooled to xe2x88x9278xc2x0 C. and added to a suspension of 132 g (0.566 moles) of ZrCl4 in 500 ml of CH2Cl2, in a 2L 3-necks round bottom flask, previously cooled to xe2x88x9278xc2x0 C. A bright yellow suspension was rapidly obtained. Said suspension was allowed to warm slowly to 20xc2x0 C. and was stirred for further 16 hours, at 20xc2x0 C. The solvent was then removed under vacuum, to give a light yellow powder. The pure final product was separated from LiCl and from polymeric byproducts by Soxhlet extraction with CH2Cl2, thus obtaining 197 g of 1,2-ethylene-bis(2-indenyl)zirconium dichloride (yield of 83% wt.).
1H NMR (C6D6): xcex4 7.5 (dd, 4H), 6.95 (dd, 4H), 5.85 (s, 4H), 2.52 (s, 4H).
1H NMR (CD2Cl): xcex4 7.5 (dd, 4H), 7.15 (dd, 4H), 6.42 (s, 4H), 3.33 (s, 4H).
13C NMR (CD2Cl2): xcex4 140.6 (2C), 129.4 (4C), 126.1 (4CH), 125.5 (4CH), 103.1 (4CH), 31.1 (2CH2).
Elemental analysis:
Calculated: C 57.40; H 3.85. Found: C 57.29; H 4.00.
1,2-ETHYLENE-BIS(2-INDENYL)ZIRCONIUM DIMETHYL
150 mg of 1,2-ethylene-bis(2-indenyl)zirconium dichloride, obtained as described in Synthesis 1, were suspended in 10 ml toluene and cooled to xe2x88x9278xc2x0 C. 2 equivalents of MeLi we re added and the reaction mixture was allowed to warm to room temperature. The reaction mixture was centrifuged and toluene was removed in vacuum, thus obtaining 80 mg of 1,2-ethylene-bis(2-indenyl)zirconium dimethyl.
1H NMR (C6D6): xcex4 7.33 (m, 4H), 6.8 (m, 4H), 5.73 (s, 4H, xe2x95x90CH), 2.29 (m, 4H, CH2 bridge), xe2x88x921.02 (s, 6H, Zr-Me).
Rac- AND meso-1,2-ETHYLENE-BIS(1-METHYL-2-INDENYL) ZIRCONIUM DICHLORIDE
(a) Preparation of the ligand 1,2-bis(1-methyl-2-indenyl)ethane
1.5 g (5.8 mmol) of 1,2-bis(2-indenyl)ethane, prepared as described in the above reported Synthesis 1(a), was dissolved in 25 ml THF and cooled to 0xc2x0 C. n-BuLi (7.4 ml of a 1.6 M solution in hexane) was added and the resulting orange/brown solution stirred for 1 hour. This was added via a cannula to a solution of MeI (0.9 ml, 14.5 mmol) dissolved in 10 ml THF, at 0xc2x0 C. After 2 hours, the THF was removed under vacuum and Et2O was added. This Et2O solution was washed 3 times with a saturated solution of NaHCO3 and 3 times with a saturated aqueous solution of NaCl. After drying over MgSO4, 1.4 g of yellow crystalline 1,2-ethylene-bis(1-methyl-2-indenyl)ethane was obtained. The ratio of double bond isomers is ca. 10:1. NMR data are reported for the major double bond isomer, i.e. the rac-isomer.
1H NMR (CDCl3): xcex4 7.45-7.10 (m, 8H), 6.53 (s, 2H), 3.43-3.30 (m, 2H, CHMe), 2.90-2.60 (m. 4H, CH2-bridge), 1.36 (d, 6H, 7.5 Hz, Me).
13C NMR (CDCl3): xcex4 154.7 (C), 148.8 (C), 144.0 (C), 126.5 (CH), 124.8 (CH), 123.9 (CH), 122.5 (CH), 120.0 (xe2x95x90CH), 46.2 and 46.0 (asymmetric CHMe), 28.1 (CH2-bridge), 15.8 (Me).
(b) Preparation of the zirconocene
4.1 ml of a solution 2.5 M of n-BuLi in hexane were added to 1.4 g 1,2-ethylene-bis(1-methyl-2-indenyl)ethane, prepared as described above, in 50 ml Et2O cooled to 0xc2x0 C. After 45 minutes, Et2O was removed in vacuum and the resulting dianion was suspended in 80 ml toluene, at 20xc2x0 C., in a drybox. 1.15 g (4.93 mmol) of ZrCl4, in the form of a slurry in 10 ml toluene, were added and the reaction mixture changed from yellow to dark brown. After stirring for 21 hours at 20xc2x0 C., the toluene solution was separated by centrifugation and the remaining solid was extracted with 3xc3x9725 ml toluene. The toluene extracts were combined, concentrated and crystallized at xe2x88x9235xc2x0 C., thus giving 300 mg of rac-1,2-ethylene-bis(1-methyl-2-indenyl)zirconium dichloride. The toluene-insoluble precipitate obtained from the reaction mixture was extracted with CH2Cl2; CH2Cl2 was removed in vacuum, thus giving a yellow powder. This was washed with 2xc3x975 ml pentane to afford 230 mg of pure meso-1,2-ethylene-bis(1-methyl-2-indenyl)zirconium dichloride.
Rac-isomer:
1H NMR (C6D6): xcex4 7.54-7.34 (m, 4H), 7.21-7.10 (m, 4H), 6.16 (s, 2H, xe2x95x90CH), 3.63-3.45 (m, 2H, CH2 bridge), 3.20-3.03 (m, 2H, CH2 bridge), 2.48 (s, 6H, Me).
13C NMR (CD2Cl2): xcex4 137.7 (C), 129.8 (C), 128.9 (C), 126.2 (CH), 125.6 (CH), 125.4 (CH), 123.5 (CH), 116.3 (C-Me), 97.9 (CH), 27.6 (CH2-bridge), 11.81 (Me).
Elemental analysis:
Calculated: C 59.18; H 4.51. Found: C 58.94; H 4.57.
Meso-isomer:
1H NMR (C6D6): xcex4 7.54-7.46 (m, 2H), 7.41-7.33 (m, 2H), 7.24-7.06 (m, 4H), 6.71 (s, 2H, xe2x95x90CH), 3.55-3.25 (m, 4H, CH2 bridge), 2.44 (s, 6H, Me).
13C NMR (CD2Cl2): xcex4 137.1 (C), 130.3 (C), 128.1 (C), 126.3 (CH), 125.8 (CH), 125.3 (CH), 123.6 (CH), 116.6 (C-Me), 101.0 (CH), 28.9 (CH2-bridge), 11.79 (Me).
Rac- AND meso-1,2-ETHYLENE-BIS(1-METHYL-2-INDENYL) ZIRCONIUM DIMETHYL
20 mg of rac- and 20 mg of meso-1,2-ethylene-bis(1-methyl-2-indenyl)zirconium dichloride, obtained as described in Synthesis 3, were separately suspended in 1 ml of C6D6, in different NMR tubes. About 5 mg of MeLi in excess, in the form of a white powder, were added to each NMR tube in the drybox. Occasional shaking of the NMR tube gave within 2 hours clean conversion to the corresponding rac- and meso-1,2-ethylene-bis(1-methyl-2-indenyl)zirconium dimethyl isomers.
Rac-isomer:
1H NMR (C6D6): xcex4 7.45-7.30 (m, 4H), 6.98-6.85 (m, 4H), 5.50 (s, 2H, xe2x95x90CH), 2.63-2.3 (m, 4H, CH2 bridge), 2.09 (s, 6H, Me), xe2x88x921.02 (s, 6H, Zr-Me).
13C NMR (C6D6): xcex4 129.6 (C), 125.2 (CH), 124.8 (C), 123.4 (CH), 122.6 (CH), 110.0 (5 ring C-Me), 97.6 (5-ring CH), 40.1 (Zr-Me), 26.8 (CH2-bridge), 10.8 (Me).
Meso-isomer:
1H NMR (C6D6): xcex4 7.42 (d, 2H), 7.30 (d, 2H), 7.04 (t, 2H), 6.9 (t, 2H), 5.93 (s, 2H, xe2x95x90CH), 2.6-2.3 (m, 4H, CH2 bridge), 2.03 (s, 6H, Me), xe2x88x920.38 (s, 3H, Zr-Me), xe2x88x921.82 (s, 3H, Zr-Me).
13C NMR (C6D6): xcex4 129.2, 127.4, 125.6, 125.0, 123.7, 123.2, 121.9, 108.6 (5 ring C-Me), 97.8 (5 ring CH), 44.1 (Zr-Me), 37.0 (Zr-Me), 27.5 (CH2-bridge), 11.6 (Me).
Rac- AND meso-1,2-ETHYLENE-BIS(1-ETHYL-2-INDENYL) ZIRCONIUM DICHLORIDE
(a) Preparation of the ligand 1,2-bis(1-ethyl-2-indenyl)ethane
1.36 g, 5.26 mmol of 1,2-bis(2-indenyl)ethane, prepared as described in the above reported Synthesis 1(a), were dissolved in 25 mL THF and cooled to xe2x88x9210xc2x0 C. 5.5 ml of a 1.6 M solution of BuLi in hexane (8.8 mmoles) were added and the resulting orange/brown solution was stirred for 2 hours, at room temperature. To the obtained mixture was added, by means of a cannula, a solution of 1.1 ml of EtI (7.1 mmol) in 10 ml THF, at xe2x88x9210xc2x0 C. After 2 hours, the THF was removed under vacuum, and Et2O was added. The thus obtained etcher solution was washed 3 times with a saturated solution of NaHCO3 and 3 times with a saturated aqueous solution of NaCl. After drying over MgSO4, 1.46 g of 1,2-bis(1-ethyl-2-indenyl)ethane was isolated, in the form of a yellow oil. 1H NMR and GC showed that it consisted of the three possible double bond isomers.
(b) Preparation of the zirconocene
4.5 ml of a 1.6 M solution of n-BuLi in hexane (7.2 mmol) were added to a suspension of 1.16 g (3.5 mmoles) of 1,2-bis(1-ethyl-2-indenyl)ethane, obtained as described above, in 50 ml of Et2O, at xe2x88x9210xc2x0 C. The mixture was maintained under stirring for 45 minutes and Et2O was removed in vacuum; the thus obtained dianion was suspended in 80 ml of toluene, at 20xc2x0 C. in a drybox. A slurry of 1.16 g (4.93 mmoles) of ZrCl4 in 10 ml of toluene was added to the reaction mixture, which turned from yellow to dark brown. After stirring for 21 hours, at 20xc2x0 C., the toluene solution was separated by centrifugation and the remaining solid was extracted with toluene (3xc3x9725 ml). The toluene extracts were combined, concentrated and crystallized at xe2x88x9235xc2x0 C., thus giving 72 mg of rac-1,2-ethylene-bis(1-ethyl-2-indenyl)zirconium dichloride.
The toluene-insoluble precipitate, obtained from the reaction mixture, was extracted with CH2Cl2; after removal of the CH2Cl2 in vacuum, a yellow powder was obtained, which was washed with pentane (2xc3x975 ml) to give 300 mg of pure meso-1,2-ethylene-bis(1-ethyl-2-indenyl)zirconium dichloride.
Rac-isomer:
1H NMR (d8-THF): xcex4 7.42 (d, 2H), 7.3 (d, 2H), 7.06-6.94 (m, 4H), 6.23 (s, 2H, xe2x95x90CH), 3.62-3.50 (m, 4H, CH2 bridge), 3.4-2.93 (m, 2H, CH2 bridge), 2.88 (dq, 2H), 1.06 (t, 6H, Me).
13C NMR (d8-THF): xcex4 137.0 (C), 130.0 (C), 128.0 (C), 127.0 (CH), 126.0 (CH), 125.5 (CH), 124.0 (CH), 122.8 (C-Me), 98.0 (CH), 27.0 (CH2-bridge), 20.7 (CH2), 16.0 (Me).
Meso-isomer:
1H NMR (CD2Cl2): xcex47.51(m, 2H), 7.37 (m, 2H), 7.20-7.07 (m, 4H), 6.73 (s, 2H, xe2x95x90CH), 3.50-3.28 (m, 4H, CH2 bridge), 3.12-3.00 (dq, 2H), 2.81-2.69 (dq, 2H) 1.14 (t, 6H, Me).
13C NMR (CD2Cl2): xcex4 135.0 (C), 129.9 (C), 125.6 (C), 125.0 (CH), 124.3 (CH), 123.0 (CH), 122.9 (CH), 122.1 (C-Me), 100.8 (CH), 28.9 (CH2-bridge), 20.0 (CH2), 11.8 (Me).
Meso-1,2-ETHYLENE-BIS(1-ETHYL-2-INDENYL) ZIRCONIUM DIMETHYL
20 mg of meso-1,2-ethylene-bis(1-ethyl-2-indenyl)zirconium dichloride, prepared as described in the above reported Synthesis 5, were suspended in 1 ml of C6D6 in a NMR tube. About 5 mg of MeLi in excess, in the form of a white powder, were added in the drybox. Occasional shaking of the NMR tube gave within 2 hours the final product meso-1,2-ethylene-bis(1-ethyl-2-indenyl)zirconium dimethyl.
1H NMR (C6D6): xcex4 7.42 (d, 2H), 7.30 (d, 2H), 7.04 (t, 2H), 6.9 (t, 2H), 5.95 (s, 2H, xe2x95x90CH), 2.8-2.2 (m, 4H, CH2 bridge+m, 4H, CH2Me), 1.0 (t, 6H, Me), xe2x88x920.4 (s, 3H, Zr-Me), xe2x88x921.9 (s, 3H, Zr-Me).
1,2-ETHYLENE-BIS(1,3-DIMETHYL-2-INDENYL) ZIRCONIUM DICHLORIDE
(a) Preparation of the ligand 1,2-bis(1,3-dimethyl-2-indenyl)ethane
Preparation of 1,2-bis(1-methyl-2-indenyl)-ethane 
10 g (38.7 mmoles) of 1,2-bis(2-indenyl)ethane, prepared as described in the above Synthesis 1(a), were suspended in 100 mL THF and to the obtained mixture were added 32 mL n-BuLi (2.5 M solution in hexane), during 15-minutes, at 0xc2x0 C. The resulting solution was allowed to warm to 20xc2x0 C. and maintained under stirring for 30 minutes at 20xc2x0 C.; to the thus obtained red/brown solution, previously cooled to 0xc2x0 C., were then added, over a few minutes, 6.0 mL MeI in 50 mL THF (also previously cooled to 0xc2x0 C.). The reaction mixture was allowed to warm to 20xc2x0 C. and was maintained under stirring for 2 hours. Subsequently, the solvent were removed in vacuum. The thus obtained sticky yellow/orange solid was dissolved in 200 mL Et2O and extracted 3 times with a saturated aqueous solution of NaHCO3 and a saturated solution of NaCl. The aqueous and organic layers were separated and Et2O was removed in vacuum, thus yielding 9.7 g (yield of 88%) of 1,2-bis(1-methyl-2-indenyl)ethane. This product consisted of a mixture of the 3 isomers reported above, wherein the double bond isomeric moieties I and II, reported below, are formed in a ratio of about 1:10 (confirmed by 1H-NMR analysis): 
1H NMR (CDCl3): xcex4 1.36 (d, J=7.5 Hz, 6H, CH3 (isomer II)), 2.09 (s, 6H, CH3 (isomer I)), 2.60-2.90 (m, 4H, CH2-bridge), 3.30-3.43 (s, 4H (isomer I) and d, 2H (isomer II)), 6.53 (s, 2H, xe2x95x90CH 5-ring), 7.10-7.45 (m, 8H, aromatic H) ppm.
Preparation of 1,2-bis(1,3-dimethyl-2-indenyl)ethane
1,2-Bis(1-methyl-2-indenyl)ethane (9.7 g, 33.9 mmol), obtained as described above, was suspended in 100 mL THF and to the obtained mixture were added 28.5 mL n-BuLi (in the form of a 2.5M hexane solution), over a period of 10 minutes, at 0xc2x0 C. The reaction mixture was allowed to warm to 20xc2x0 C. and maintained under stirring for 90 minutes, at 20xc2x0 C.; to the thus obtained red/brown solution, previously cooled to 0xc2x0 C., were added, over few minutes, 5.3 mL MeI in 50 mL THF (also previously cooled to 0xc2x0 C.). The reaction mixture was allowed to warm to 20xc2x0 C. and was-maintained under stirring for 2 hours. After removal of the solvent in vacuum, the thus obtained sticky yellow/orange solid was dissolved in 200 mL Et2O and extracted 3 times with a saturated aqueous solution of NaHCO3 and a saturated aqueous solution of NaCl. The aqueous and organic layers were separated and Et2O was removed in vacuum; the resulting yellow sticky solid was washed with hexane, to give 2.3 g of 1,2-bis(1,3-dimethyl-2-indenyl)ethane (24% yield).
(b) Preparation of the zirconocene
Preparation of the dianion of 1,2-bis(1,3-dimethyl-2-indenyl)ethane
1.47 g (4.68 mmol) of 1,2-bis(1,3-dimethyl-2-indenyl)ethane were dissolved in 30 mL Et2O and to the obtained solution were added 3.9 mL n-BuLi (as a solution 2.5 M in hexane), at xe2x88x9278xc2x0 C., over a period of 5 minutes. The reaction mixture was maintained under stirring for 30 minutes, at xe2x88x9278xc2x0 C., and then was allowed to warm to 20xc2x0 C. A precipitate formed during the reaction. The thus obtained orange/brown reaction mixture was filtered and the solid was washed with 20 ml hexane, in order to remove 1,1xe2x80x2-dimethylated products, thus giving the dianion of 1,2-bis(1,3-dimethyl-2-indenyl)ethane, in the form of a white/yellow solid, which was used without further purification for the subsequent reaction with ZrCl4, as described below.
1H NMR (d8-THF): xcex4 2.43 (s, 12H, CH3), 3.01 (s, 4H, CH2 bridge), 6.25 (m, 4H, aromatic H), 7.03 (m, 4H, aromatic H) ppm.
Preparation of 1,2-ethylene-bis(1,3-dimethyl-2-indenyl)zirconium dichloride
The dianion of 1,2-bis(1,3-dimethyl-2-indenyl)ethane, obtained as described above, was suspended in 30 mL toluene and to the obtained mixture was added, at xe2x88x9230xc2x0 C., over a period of few minutes, a suspension of 0.95 g (4.08 mmol) of ZrCl4 in 10 ml toluene.
The reaction mixture was allowed to warm to 20xc2x0 C. and the color changed to orange. The mixture was maintained under stirring overnight and was subsequently filtered; the obtained solid was extracted with toluene (3xc3x9710 ml). After removal of the solvent in vacuum, the obtained solid was washed with hexane, to afford 206 mg of 1,2-ethylene-bis(1,3-dimethyl-2-indenyl)zirconium dichloride, as an orange powder.
1H NMR (CD2Cl2): xcex4 2.59 (s, 12H, CH3), 3.50 (s, 4H, CH2 bridge), 7.16 (m, 4H, aromatic H), 7.45 (m, 4H, aromatic H) ppm.
Rac- AND meso-1,2-ETHYLENE-BIS(4-PHENYL-2-INDENYL) ZIRCONIUM DICHLORIDE
(a) Preparation of the ligand 1,2-bis(4-phenyl-2-indenyl)ethane
This ligand was prepared through the intermediate 2,5-bis(2-phenyl-benzyl) adipic acid diethylester, synthesized according to the following reaction scheme: 
Into a 3 neck flask, equipped with water cooler, were added 43.8 mL (0.22 mol) of diethyladipate and 220 mL THF. 16.3 g (0.24 mol, 1.1 equivalents) of NaOEt were added in small portions, at 20xc2x0 C., and the reaction mixture was stirred at 60xc2x0 C. for 16 hours. After cooling to 20xc2x0 C., 48.6 g (0.20 mol) of 2-phenyl-benzyl bromide was added dropwise. The reaction mixture was stirred at 60xc2x0 C., for 16 hours, to give 2-(2-phenyl-benzyl) adipic acid diethylester as a viscous oil, in a yield of 92%.
1H NMR (CDCl3): xcex4 1.08 (t, 3H, CH3), 1.21 (t, 3H, CH3), 1.28-1.45 (q, 2H, CH2 and m, 2H, CH2), 2.11 (t, 2H, CH2), 2.37 (m, 1H, CH), 2.85 (d, 2H, CH2), 3.97 (q, 2H, CH2), 4.08 (q, 2H, CH2), 7.16-7.48 (m, 9H, CH) ppm.
13C NMR (CDCl3): xcex4 14.05 (CH2Me), 14.17 (CH2Me), 22.41 (CH2), 31.39 (CH2), 33.86 (CH2), 35.60 (CH2), 46.01 (CH), 60.03 (CH2CH3), 60.14 (CH2CH3), 126.28 (CH), 126.90 (CH), 127.23 (CH), 128.11 (CH), 129.12 (CH), 129.71 (CH), 130.08 (CH), 136.62 (C), 141.56 (C), 142.24 (C), 173.13 (CO2Et), 175.22 (CO2Et).
Under the operating conditions reported above, to the obtained diethylester were sequentially added 14.9 g (0.22 mol) of NaOEt and 44.4 g (0.18 mol) of 2-phenyl-benzyl bromide; the obtained mixture was stirred for 16 hours, at 60xc2x0 C. After the addition of dilute HCl to neutralize the base, the THF and the aqueous acidic phases were separated. The aqueous acidic layer was extracted 3 times with CH2Cl2. The combined THF and CH2Cl2 extracts were evaporated to dryness, to give the intermediate 2,5-bis(2-phenyl-benzyl) adipic acid diethylester, in the form of a very viscous oil.
Said intermediate 2,5-bis(2-phenyl-benzyl) adipic acid diethylester was then reacted according to the following reaction scheme: 
To the 2,5-bis(2-phenyl-benzyl) adipic acid diethylester, obtained as described above, were added 180 mL of a solution of 6 M KOH in H2O/MeOH and the reaction mixture was refluxed for 16 hours. MeOH was removed on a rotary evaporator and the aqueous layer was washed with Et2O (2xc3x97200 mL). The alkaline aqueous layer was acidified, at 0xc2x0 C., with HCl 37% to pH 1. A white/yellow powder was formed, filtered off and washed with water and a little hexane. Said powder was thoroughly dried, to afford 77.0 g of 2,5-bis(2-phenyl-benzyl) adipic acid (85% yield). 
1H NMR (d8-THF): xcex4 1.00-1.30 (m, 4H, CH2), 2.22 (m, 2H, CH), 2.60 (m, 2H, CH2), 2.76 (m, 2H, CH2), 7.05-7.39 (m, 18H, CH), 10.45 (s, 2H, OH) ppm.
13C NMR (d8-THF): xcex4 30.81 (CH2;C), 36.18 (CH2; A), 36.34 (CH2*;A), 47.04 (CH; B), 47.24 (CH *;B), 127.02 (CH), 127.88 (CH), 128.20 (CH), 129.15 (2xc3x97CH), 130.37 (2xc3x97CH), 130.77 (CH), 131.00 (CH), 138.49 (C), 143.20 (C), 143.68 (C), 176.50 (CO2H) ppm.
In a 1 L flask equipped with a reflux condenser, containing 77.0 g (0.16 mol) of 2,5-bis(2-phenyl-benzyl) adipic acid, obtained as described above, were added 150 mL (2.06 mol) of SOCl2). A white suspension was obtained, which was warmed to 50xc2x0 C. and became a yellow solution, with concomitant evolution of HCl and SO2. After gas evolution had finished, the excess SOCl2 was removed under vacuum. To the obtained mixture were then added 100 mL of toluene, which was subsequently removed under vacuum to ensure complete removal of SOCl2. 2,5-bis(2-phenyl-benzyl) adipic acid dichloride (82.9 g, yield of 100%) was isolated, in the form of a viscous beige oil. 
1H NMR (CDCl3): xcex4 1.17 (m, 2H, CH2), 1.36 (m, 2H, CH2), 2.64 (m, 2H, CH), 2.85 (dd, 2H, CH2), 3.07 (m, 2H, CH2), 7.20-7.55 (m, 18H, aromatic. CH) ppm.
13C NMR (CDCl3): xcex4 28.39 (CH2;C), 35.06 (CH2; A), 35.14 (CH2*;A), 57.28 (CH; B), 57.46 (CH *;B), 127.22 (CH), 127.41 (CH), 127.80 (aromatic. CH), 128.56 (2xc3x97CH), 129.14 (2xc3x97CH), 129.94 (CH), 130.53 (CH), 134.58 (C), 141.11 (C), 142.29 (C), 175.89 (COCl; D), 175.93 (COCl *;D) ppm.
To a suspension of 56.0 g (0.42 mol) of AlCl3 in 40 mL CH2Cl2, under nitrogen, was added at 20xc2x0 C., 82.9 g (0.16 mol) of 2,5-bis(2-phenyl-benzyl) adipic acid dichloride, obtained as described above, diluted in 250 mL CH2Cl2 (1.3 eq. AlCl3 per acid chloride group). After addition was completed, the reaction mixture was maintained under stirring for 5 minutes and then poured onto ice. CH2Cl2 was separated from the water layer and the water layer was extracted with 2xc3x97200 mL CH2Cl2. The combined CH2Cl2 layers were washed with a saturated solution of NaHCO3. CH2Cl2 was removed under vacuum and the resulting powder was washed with a little hexane, to give 63.3 g of the 1,2-bis(4-phenyl-indanonyl)ethane (89% yield). 
1H NMR (CDCl3): xcex4 1.55 (m, 2H, CH2), 2.07 (m, 2H, CH2), 2.63 (m, 2H, CH2), 2.86 (m, 2H, CH), 3.36 (dd, 2H, CH2, J=18 Hz), 7.10-7.86 (m, 16H, aromatic. CH) ppm.
13C NMR (CDCl3): xcex4 28.60 (CH2; C), 29.51 (CH2 *;C), 32.44 (CH2; A), 32.75 (CH2*;A), 47.19 (CH; B), 47.82 (CH *;B), 122.77 (CH; F), 122.84 (CH *;F), 127.67 (CH), 127.97 (CH), 128.42 (2xc3x97CH), 128.62 (2xc3x97CH), 134.86 (CH), 137.04 (C; G), 137.10 (C *;G), 138.99 (C), 140.25 (C; E), 140.27 (C *;E), 151.01 (C), 208.32 (Cxe2x95x90O; D), 208.42 (Cxe2x95x90O *;D) ppm.
20.0 g (0.045 mol) of 1,2-bis(4-phenyl-indanonyl)ethane, obtained as described above, were dissolved in 310 mL of dry THF, and the obtained solution was slowly added, over a period of 20 minutes, via a cannula, to a suspension of 1.85 g (0.049 mol, 1.09 eq.) of LiAlH4 in 80 mL THF, contained in a 1L round-bottom flask, previously cooled to 0xc2x0 C. At the end of the addition, the reaction mixture was maintained under stirring for 45 minutes, at 20xc2x0 C. THF was removed under vacuum and, after the addition of ice and diluted HCl, the resulting suspension was acidified to pH 1. The thus obtained mixture was then filtered, to give 1,2-bis(4-phenyl-2-indanolyl)ethane, in the form of an off-white powder. After washing with water, the product was dried to give 18.3 g of 1,2-bis(4-phenyl-2-indanolyl)ethane (yield 91%). 
1H-NMR (CDCl3): xcex4 1.40-2.22 (m, 8H, 3xc3x97CH2, 2xc3x97OH), 2.55 (m, 2H, CH), 3.11 (dd, 2H, CH2, J=18 Hz), 4.85 (m, 2H, CHxe2x80x94OH), 7.10-7.50 (16H, aromatic. CH) ppm.
13C-NMR (d8-THF): xcex4 33.20 (CH2; C), 33.38 (CH2 *;C), 37.04 (CH2; A), 52.64 (CH; B), 52.86 (CH *;B), 81.94 (C-OH), 123.80 (CH), 127.84 (2xc3x97CH), 128.44 (CH), 129.30 (2xc3x97CH), 129.64 (2xc3x97CH), 139.22 (CH), 140.06 (C), 142.34 (C), 148.96 (C; D), 149.03 (CH *;D).
11.0 g (0.025 mol) of 1,2-bis(4-phenyl-2-indanolyl)ethane, obtained as described above, were put into a 1 L 3-neck round-bottom flask and heated to 345xc2x0 C., for 20 minutes, under a slow steam of N2. After cooling, a yellow glass was obtained, which was dissolved in CH2Cl2. After removal of the CH2Cl2 under vacuum, 8.8 g of 1,2-bis(4-phenyl-2-indenyl)ethane (87% yield) were isolated, in the form of a yellow powder consisting of a mixture of two double-bond isomers. 
Isomer 1:
1H NMR (CDCl3): xcex4 2.82 (s, 4H, CH2), 3.46 (s, 4H, CH2), 6.64 (s, 2H, CH), 7.14-7.59 (m, 16H, CH) ppm.
13C NMR (CDCl3): xcex4 30.57 (CH2), 41.11 (CH2), 119.25 (CH), 124.47 (CH), 126.73 (CH), 127.02 (2xc3x97CH), 128.37 (2xc3x97CH), 137.48 (C), 140.46 (C), 141.23 (C), 145.96 (C), 149.90 (q, C 5-ring) ppm.
Isomer 2:
1H NMR (CDCl3): xcex4 2.82 (s, 4H, CH2), 3.46 (s, 4H, CH2), 6.76 (s, 2H, CH), 7.14-7.59 (m, 16H, (CH) ppm.
13C NMR (CDCl3): xcex4 30.69 (CH2), 41.32 (CH2), 119.25 (CH), 122.43 (CH), 124.09 (CH), 128.61 (2xc3x97CH), 128.81 (2xc3x97CH), 134.23 (C), 141.00 (C), 143.06 (C), 143.63 (C), 150.11 (q, C 5-ring) ppm.
(b) Preparation of the zirconocene
465 mg, 1.13 mmol of 1,2-bis(4-phenyl-2-indenyl)ethane, prepared as described above, were dissolved in 20 mL Et2O, in a Schlenk tube, and cooled to xe2x88x9278xc2x0 C. 0.95 mL of n-BuLi as a solution 2.5 M in hexane (2.38 mmol; 2.1 equiv.) was added dropwise. The reaction mixture was allowed to warm to 20xc2x0 C. Et2O was removed under vacuum, to afford the dianion, in the form of a light-yellow powder.
1H NMR (d8-THF): xcex4 3.22 (s, 4H, CH2), 5.85 (ds, 2H, CH), 6.08 (ds, 2H, CH), 6.35 (m, 4H, aromatic CH), 7.08 (m, 4H, aromatic CH), 7.28 (t, 4H, aromatic CH), 7.74 (d, 4H, arom. CH) ppm.
The above obtained dianion was suspended in toluene and cooled to xe2x88x9220xc2x0 C.; to the obtained mixture were added 0.28 g (1.19 mmol; 1.05 equivalents) of ZrCl4. The reaction mixture was maintained under stirring for 16 hours, at 20xc2x0 C.; then it was centrifuged and the toluene layer was discarded. The remaining powder was washed with toluene (20 mL) and then extracted with CH2Cl2, in order to separate the product from LiCl. A pure mixture of rac and meso-isomers of 1,2-ethylene-bis(4-phenyl-2-indenyl)zirconium dichloride was obtained, in the form of a yellow powder. By crystallization from toluene, the meso isomer could be completely separated from the rac-isomer. The rac-isomer was obtained as a rac:meso mixture of about 4:1.
Rac-isomer:
1H NMR (C6D6): xcex4 2.48 (ds, 4H, CH2-bridge), 5.53 (ds, 2H, CH, J=2.1 Hz), 6.37 (ds, 2H, CH, J=2.1 Hz), 6.90-7.70 (m, 16H, arom. CH) ppm.
1H NMR (CD2Cl2): xcex4 3.39 (m, 4H, CH2-bridge), 6.35 (ds, 2H, CH, J=2.1 Hz), 6.70 (ds, 2H, CH, J=2.1 Hz), 7.22-7.76 (m, 16H, arom. CH) ppm.
13C NMR (CD2Cl2): xcex4 30.81 (CH2), 100.38 (CH), 103.94 (CH), 124.52, 125.89, 126.19, 127.65, 128.55, 129.15, 130.30, 139.58, 140.36, 140.51 ppm.
Meso-isomer:
1H NMR (C6D6): xcex4 2.41 (m, 4H, CH2-bridge), 5.95 (ds, 2H, CH, J=2.1 Hz), 6.39 (ds, 2H, CH, J=2.1 Hz), 6.85-7.62 (m, 16H, arom. CH) ppm.
1H NMR (CD2Cl2): xcex4 3.37 (s, 4H, CH2-bridge), 6.41 (ds 2H, CH, J=2.1 Hz), 6.78 (ds, 2H, CH, J=2.1 Hz), 7.19-7.64 (m, 16H, arom. CH) ppm.
13C NMR (CD2Cl2): xcex4 30.63 (CH2), 101.28 (CH), 105.85 (CH), 139.57, 139.58, 139.70 ppm.
Meso-1,2-ETHYLENE-BIS(4-PHENYL-2-INDENYL) ZIRCONIUM DIMETHYL
Meso-1,2-Ethylene-bis(4-phenyl-2-indenyl)zirconium dichloride, obtained as described in the above Synthesis 9, were suspended in C6D6 and MeLi in excess was added; after 30 minutes at 20xc2x0 C., meso-1,2-ethylene-bis(4-phenyl-2-indenyl)zirconium dimethyl was obtained.
1H NMR (C6D6): xcex4 xe2x88x921.83 (s, 3H, CH3), 0.28 (s, 3H, CH3), 2.28 (ds, 4H, CH2-bridge, J=4.5 Hz), 5.90 (ds, 2H, CH, J=2.1 Hz), 6.24 (ds, 2H, CH, J=2.1 Hz), 6.89-7.48 (m, 16H, arom. CH) ppm.
Rac- AND meso-1,2-ETHYLENE-BIS(1-METHYL-4-PHENYL-2-INDENYL) ZIRCONIUM DICHLORIDE
(a) Preparation of the ligand 1,2-bis(1-methyl-4-phenyl-2-indenyl)ethane
The ligand was prepared according to the following reaction scheme: 
To a solution of 67.8 mL MeMgBr (3M in ether) in 100 mL Et2O was added a solution of 15 g (33.9 mmol) of 1,2-bis(4-phenyl-indanonyl)ethane, prepared as described in the above synthesis 8(a), in 150 mL THF, over a period of 45 minutes, at 0xc2x0 C. The formation of a white/beige precipitate was observed. The reaction mixture was allowed to warm to 20xc2x0 C. and was maintained under stirring for 2 hours. The reaction mixture was then poured into ice and acidified to pH 1, with 37% HCl, and finally extracted with Et2O. The organic layer was extracted with a saturated solution of NaCl and the solvent was removed in vacuum. The formed diol was dissolved in CH2Cl2 and p-toluene-sulfonic acid was added. The mixture was stirred overnight at 20xc2x0 C. The solution was dried over MgSO4, filtered and the solvent was removed in vacuum, thus yielding 9.0 g of the ligand 1,2-bis(1-methyl4-phenyl-2-indenyl)ethane (69% yield).
1H NMR (CD2Cl2): xcex4 2.08 (s, 6H, CH3), 2.69 (s, 4H, CH2 bridge), 3.43 (ds, 4H, CH2 5-ring), 7.2-7.6 (m, 16H, aromatic H) ppm.
(b) Preparation of the zirconocene
To a solution of 0.54 g (1.23 mmol) of 1,2-bis(1-methyl-4-phenyl-2-indenyl)ethane, prepared as described above, in 20 mL Et2O, was added 1.1 mL of n-BuLi (in the form of a 2.5M solution in hexane), at xe2x88x9278xc2x0 C. The reaction mixture was allowed to warm to 20xc2x0 C.; the formation of a precipitate was observed and the color changed to orange/red. The reaction mixture was stirred for 2 hours, at 20xc2x0 C., and the solvent was removed in vacuum. The dianion was obtained in the form of a sticky product; after washing with hexane, the orange powder was suspended in 10 mL toluene and 0.29 g of ZrCl4 were added, at xe2x88x9230xc2x0 C. The reaction mixture was allowed to warm to 20xc2x0 C. and was stirred overnight. The thus obtained orange suspension was filtered and the filtrate was concentrated and used for crystallization.
The crude product was 1,2-ethylene-bis(1-methyl4-phenyl-2-indenyl)zirconium dichloride, as a mixture of rac/meso isomers in a 1:1 ratio. By successive crystallizations, it could be obtained as a 4:1 rac/meso mixture. Crystallization from dichloromethane/hexane mixture gave 94% pure meso-isomer.
Rac isomer:
1H NMR (CD2Cl2): xcex4 2.34 (s, 6H, CH3), 3.14-3.59 (m, 4H, CH2 bridge, symmetric pattern), 6.44 (s, 2H, CH 5-ring), 7.10-7.70 (m, 16H, aromatic H) ppm.
Meso isomer:
1H NMR (CD2Cl2): xcex4 2.48 (s, 6H, CH3), 3.20-3.50 (m, 4H, CH2 bridge, symmetric pattern), 6.90 (s, 2H, CH 5-ring), 7.10-7.70 (m, 16H, aromatic H) ppm.
Rac- AND meso-1,2-ETHYLENE-BIS(1-ISOPROPYL-4-PHENYL-2-INDENYL) ZIRCONIUM DICHLORIDE
(a) Preparation of the ligand 1,2-bis(1-isopropyl-4-phenyl-2-indenyl)ethane
The ligand was prepared according to the following reaction scheme: 
In a 250 mL flask, containing 40 mL of a solution 2.0 M of i-PrMgCl in Et2O (9 equivalents), previously cooled to 0xc2x0 C., was added dropwise, over a period of 15-20 minutes, a solution of 4 g of 1,2-bis(4-phenyl-indanonyl)ethane (9.17 mmol), prepared as described in the above synthesis 8(a), in 80 mL THF. The obtained mixture was stirred for 90 minutes and then poured onto ice. The organic layer was separated and the aqueous layer extracted with CH2Cl2. The combined organic layers were washed with a saturated solution of NaCl and then dried over MgSO4, to give the diol. This product was dissolved in 100 ml of CH2Cl2 and to the obtained solution were added 1.5 g of p-toluensulfonic acid; the reaction mixture was maintained under stirring for 20 hours, at 20xc2x0 C. The obtained mixture was dried with MgSO4, to give a clear yellow solution, which was filtered through a plug of silica to give pure 1,2-bis(1-isopropyl4-phenyl-2-indenyl)ethane.
1H NMR (CDCl3): xcex4 1.36 (d, 12H, CH3), 2.67 (s, 4H, CH2-brug), 3.18 (septet, 2H, CH), 3.36 (s, 4H, CH2), 7.13-7.52 (m, 16H, arom. CH) ppm.
13C-NMR (CDCl3): xcex4 21.13 (CH3), 26.75 (CH), 29.34 (CH2), 40.41 (CH2), 119.47 (CH), 124.24 (CH), 126.48 (CH), 126.91 (CH), 128.30 (2xc3x97CH), 128.49 (2xc3x97CH), 137.60 (q. C 5-ring), 140.64 (C), 140.98 (C), 141.41 (C), 142. 66 (C), 145.50 (q, C 5-ring) ppm.
(b) Preparation of the zirconocene
0.29 g (0.58 mmol) of 1,2-bis(1-isopropyl-4-phenyl-2-indenyl)ethane, prepared as described above, were dissolved in 30 mL Et2O and cooled to xe2x88x9278xc2x0 C. 0.5 mL of n-BuLi (in the form of a 2.5M solution in hexane) were added. The obtained yellow solution became brown-red and the reaction mixture was allowed to warm to 20xc2x0 C. The reaction mixture was stirred for 1 hour at 20xc2x0 C. and Et2O was removed in vacuum to give the dianion.
1H NMR (d8-THF): xcex4 1.4 (d, 12H, Me), 3.22 (s, 4H, bridge CH2), 3.4 (septet, 2H, CHMe2), 5.93 (s, 2H, CH), 6.28 (m, 4H, aromatic CH), 7.08 (t, 2H, aromatic CH), 7.22 (t, 2H, aromatic CH), 7.28 (t, 4H, aromatic CH), 7.66 (d, 4H, aromatic CH) ppm. The dianion was suspended in toluene and cooled to xe2x88x9230xc2x0 C.; 0. 15 g of ZrCl4 (0.64 mmol) were added and the reaction mixture was stirred for 4 hours at 20xc2x0 C. and then centrifuged. Toluene was discarded and the remaining powder was extracted with CH2Cl2. Centrifugation afforded a mixture of the two isomers rec/meso-1,2-ethylene-bis(1-isopropyl4-phenyl-2-indenyl)zirconium dichloride, about in a 1:1 ratio.
First isomer:
1H NMR (C6D6): xcex4 1.15 (d, 6H, Me), 1.58 (d, 6H, Me), 2.5 (m, 2H, bridge), 2.92 (m, 2H, bridge), 3.35 (septet, 2H, CHMe2), 6.69 (s, 1H, CH), 6.9-7.7 (m, 16H, aromatics) ppm.
Second isomer:
1H NMR (C6D6): xcex4 1.03 (d, 6H, Me), 1.09 (d, 6H, Me), 2.5 (m, 2H, bridge), 3.08 (m, 2H, bridge), 3.2 (septet, 2H, CHMe2), 6.33 (s, 1H, CH), 6.9-7.7 (m, 16H, aromatics) ppm
Rac-1,2-ETHYLENE-BIS(1-INDENYL)ZIRCONIUM DICHLORIDE (EBIZrCl2)
This zirconocene was prepared as described in the European patent application EP 0 575 875 (stages (a) and (b) of the synthesis of ethylene-bis(4,5,6,7-tetrahydroindenyl) zirconium dichloride).
METHYLENE-BIS(2-INDENYL)ZIRCONIUM DICHLORIDE
(a) Preparation of the ligand bis(2-indenyl)methane
44.3 g (335 mmol) of 1-indanone, 14.3 g (477 mmol) of paraformaldehyde and 38.4 g (471 mmol) of Me2NH.HCl were combined in 105 ml absolute EtOH and 25 drops of 37% HCl added. This was refluxed for 2.5 hours. After allowing to cool to room temperature, a copious crystalline white precipitate formed. This was filtered off and washed with hexane to give 52.2 g (69%) of the Mannich base 2-CH2N(CH3)2.HCl-1-indanone.
1H NMR (CDCl3): xcex4 9.9 (broad s, 1H, HCl), 7.73 (d, 1H), 7.62 (t, 1H), 7.5 (d, 1H), 7.38 (t, 1H), 3.8-3.2 (m, 5H), 2.95 (d, 3H, Me), 2.9 (d, 3H, Me).
13C NMR (CD2Cl2): xcex4 206.0 (CO), 154.9 (C), 136.6(CH), 135.0 (C), 128.1 (CH), 127.0 (CH), 124.3 (CH), 58.9 (CH2), 44.0 (NMe2), 34.6 (CH), 32.9 (CH2).
52.2 g (232 mmol) of the Mannich base, prepared as described above, 43.2 g (327 mmol, 1.4 equivalents) of 1-indanone and 18.2 g (325 mmol, 1.4 equivalents) of KOH were placed in a 250 ml round-bottom flask and 200 ml toluene added. This was brought to reflux whereupon the color changed from yellow to a light purple. After 3 hours reflux, the solution was allowed to cool, more KOH was added and the refluxing continued whereupon the reaction mixture became a dark purple color. This was then allowed to cool to room temperature. This was diluted with ether and washed with saturated aqueous NaHCO3 solution. The layers were separated, the water layer extracted with ether, the ether extracts were combined, and dried over MgSO4. The solvents were evaporated to give a brown oil. This proved to be a mixture of 1-indanone and product. The brown oil was washed with hexane and ether in order to extract 1-indanone. In this way, 15.1 g (24%) of pure CH2(1-indanone)2 were isolated.
1H NMR (CDCl3): xcex4 7.75 (d, 2H), 7.6 (t, 2H), 7.45 (d, 2H), 7.4 (t, 2H), 3.4 (m, 2H), 2.95 (m, 4H), 2.05 (t, 2H).
13C NMR (CDCl3): xcex4 208.7 (CO), 153.9 (C), 137.0 (C), 135.4 (CH), 128.0 (CH), 127.1 (CH), 124.5 (CH), 46.5 (CH2), 33.6 (CH).
15.0 g (54 mmol) of CH2(1-indanone)2, prepared as described above, and 24.3 g (2.4 equiv.) of tosyl hydrazine were placed in a 250 ml round-bottom flask and 100 ml EtOH added. Then 10 drops of 37% HCl were added and the reaction mixture brought to reflux under nitrogen. On coming to reflux, everything dissolved and a clear brown solution resulted. After refluxing for 10 minutes, a white jelly-like material began to precipitate. This was washed with MeOH and then dried under vacuum. This gave 21 g (63%) of the bis(hydrazone). 10.8 g (17.6 mmol) of the bis(hydrazone), suspended in 250 ml N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-ethylene diamine (TMEDA) in a large Schlenk tube, was slowly added to 15.2 g (141 mmol, 8 equivalents) of lithium diisopropylamide, dissolved in 50 ml TMEDA and cooled to 0xc2x0 C. The solution changed from yellow to purple and then to dark purple. It was allowed to warm to room temperature and then decanted onto ice to give a yellow solution. On washing with 100 ml aqueous NaHCO3 the solution became purple. This was extracted copiously (3xc3x97250 ml) with Et2O, the Et2O extracts combined and dried over MgSO4. These were evaporated to a brown oil which was extracted with pentane. Working up of the pentane extracts afforded 0.59 g (14%) of bis(2-indenyl)methane.
1H NMR (CDCl3): xcex4 7.38 (d, 2H), 7.28 (t, 2H), 7.25 (d, 2H), 7.12 (t, 2H), 6.6 (s, 2H, xe2x95x90CH), 3.65 (s, 2H, bridge CH1), 3.38 (s, 4H, 2xc3x97CH2).
13C NMR(CDCl3): xcex4 148.6 (C), 145.9 (C), 143.8 (C), 128.5 (CH), 126.8 (CH), 124.4 (CH), 124.0 (CH), 120.7 (xe2x95x90CH), 41.4 (CH2), 33.63 (CH2).
(b) Preparation of the zirconocene dichloride
0.29 g (1.19 mmol) of bis(2-indenyl)methane, prepared as described above, were dissolved in 40 ml ether and cooled to xe2x88x9278xc2x0 C. Then 1.6 ml of a 1.6 M solution of n-BuLi in hexane (2.1 equivalents) were added by syringe. It was allowed to warm to room temperature. After 90 minutes at room temperature it was cooled to xe2x88x9278xc2x0 C. and 0.29 g ZrCl4, suspended in 30 ml Et2O, was added. On allowing to warm to room temperature and stirring for 2 hours, the color changed from brown to yellowish. The solvent was removed under vacuum and the powder washed with Et2O and then hexane to give 300 mg of methylene-bis(2-indenyl)zirconium dichloride as a yellow powder.
1H NMR (CD2Cl2): xcex4 7.51 (dd, 4H), 7.24 (dd, 4H), 6.1 (s, 4H, xe2x95x90CH), 4.28 (s, 2H, bridge CH2).